This invention relates generally to tempered water mixing systems of the type used in emergency drench shower and eyewash stations, wherein cold and hot water supplies are thermostatically blended to provide a tempered discharge outflow at a selected temperature. More particularly, this invention relates to improvements in tempered water mixing systems, wherein back-up control valves are provided to permit substantial system water flows without risk of user scalding in the event of malfunction of a main thermostatic mixing valve.
Tempered water mixing systems are generally known in the art for providing a discharge outflow at a selected and relatively lukewarm, or tempered, temperature. Such mixing systems are used in a variety of commercial and/or industrial applications, particularly such as emergency drench shower stations and/or safety eyewash stations used to rinse hazardous chemicals from a person's skin and clothing. A typical system includes a thermostatic mixing valve adapted for connection to a cold water supply and a hot water supply, and including means for thermostatically and automatically blending the water inflows to produce a discharge outflow having the selected temperature. An exemplary thermostatic mixing valve of this general type is available from Powers Process Controls of Skokie, Ill., under the designation Hydroguard Series Nos. 420 and 430.
In the past, tempered water mixing systems have periodically encountered malfunction in the operation of the thermostatic mixing valve. Such malfunction can occur in any one of several modes. As one example, the mixing valve can stick in a position providing unregulated full flow of hot water, resulting in extremely undesirable and potentially dangerous scalding of a person using an emergency shower or eyewash station. In another mode, the mixing valve can stick in a position which allows unregulated full flow of cold water, whereby a person using an emergency shower or eyewash station may be subjected to undesirably cold water flow. Unfortunately, this cold water flow condition typically results in undesirably shortened flush or rinse times and can contribute to hypothermia in installations located in a cold weather climate. Another failure mode results in insufficient flow of hot or cold water, such that the discharge outflow is inadequate for proper flush flow rinsing of contaminants from a person using a drench shower or eyewash station.
Some tempered water mixing systems have been designed with back-up features intended to address the failure modes noted above. For example, solenoid operated valves have been used in combination with various temperature switches and/or flow rate switches for bypassing cold water flow past the main mixing valve when a malfunction occurs. Such devices, however, rely upon electrical power to achieve proper back-up operation. In the event of a power failure, the back-up devices in such systems have generally failed to function, or otherwise provide only for cold water flow. Moreover, during normal operation, the electrically operated components can cycle back-and-forth, so that a user is subjected to alternating brief flows of water which is either too hot or too cold. Further, electrically powered back-up devices are unacceptable for use in many industrial applications in proximity with volatile materials.
There exists, therefore, a significant need for further improvements in tempered water mixing systems particularly of the type used for emergency drench shower and eyewash stations, wherein the system includes back-up features responsive to malfunction of a main mixing valve to provide continued and substantial flow of water at a tempered temperature level. The present invention fulfills this need and provided further related advantages.